Thick metal sheets for light ships: welding steel and aluminum

Figure caption 1: Laser welding of steel to aluminum. (Photo: LZH)

Light, resource-efficient and at the same time robust - what is good for lightweight construction in the automobile industry is just as important for ship construction. Therefore, steel-aluminum joints are also used for ships. However, ships need completely different material thicknesses. The ten partners of the project LaSAAS, under the leadership of the Laser Zentrum Hannover e.V. (LZH), are dedicated to developing a robust laser welding process for the maritime manufacturing.

In times of scarce resources it is also important in the ship industry to lower fuel consumption and carbon dioxide output, in order to reduce the environmental impact. Already, components are being made using weight-reducing steel-aluminum constructions, such as ship hulls made of steel and superstructures made of aluminum. In addition, such hybrid material constructions lower the center of gravity of the ship and thus stabilize it. At the moment, the different metals are joined using an adapter piece. This is done using explosive cladding, a complicated and cost intensive joining technology.

Joining steel directly to aluminum
The scientists and industrial partners of the joint project LaSAAS want to replace this adapter piece. For this purpose, the system manufacturers Precitec GmbH & Co. KG, Scansonic MI GmbH and TRUMPF Laser- und Systemtechnik GmbH are working together with the LZH to develop a laser processing head with a weld penetration depth control.

Using this, the LZH will develop a laser welding process under lab conditions that will later be tested in cooperation with the LASER on demand GmbH. Afterwards, the process will be transferred to actual applications with the semi-finished product manufacturers Druckguss Service Deutschland GmbH and Hilbig GmbH as well as the shipyards Fr. Lürssen Werft GmbH & Co. KG and MEYER WERFT GmbH & Co. In addition, the Fraunhofer Institute for Structural Durability and System Reliability (LBF) will examine the fatigue behavior of the seams, especially under the influence of corrosive media.

Controlling the weld penetration depth
Generally, when thermally welding steel to aluminum, brittle intermetallic phases occur, so that the seams can prematurely fail under stress. However, the weld seam characteristics can be optimized based on the mix ratio of the metals, respectively the weld penetration depth. Thus, the project partners plan on controlling the weld penetration depth by analyzing the spectral process emissions and short coherence interferometry.

If successful, the process can naturally become interesting for other branches which assemble large pieces, such as train coach or commercial vehicle construction, too.

The joint project “Laser Welding of Steel to Aluminum for Applications in Shipbuilding” (LaSAAS) is funded by the German Federal Ministry for Economics and Energy (BMWi), and supervised by the Forschungszentrum Jülich GmbH (PTJ).

This press release is accompanied by one figure.
Figure caption 1: Laser welding of steel to aluminum. (Photo: LZH)

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Laser Zentrum Hannover e.V. (LZH)

As an independent, non-profit research institute, the Laser Zentrum Hannover e.V. (LZH) stands for innovative research, development and consulting. The LZH is supported by the Lower Saxony Ministry for Economics, Labour and Transport and is dedicated to the selfless promotion of applied research in the field of photonics and laser technology. Founded in 1986, over 170 employees are now working for the LZH.

The focus of the LZH lies on the fields of optical components and systems, optical production technologies, and biomedical photonics. Interdisciplinary cooperation between natural scientists and mechanical engineers makes innovative approaches to challenges from the most different areas possible: from the development of components for specific laser systems to process developments for the most diverse laser applications, for example for medical technology or lightweight construction in the automotive sector. Seventeen spin off companies have emerged from the LZH up to now. Thus, the LZH has created a strong transfer between fundamental science, application oriented research, and industry.